An automotive vehicle typically includes an internal combustion engine containing a rotary crankshaft configured to transfer motive power from the engine through a driveshaft to turn the wheels. A transmission is interposed between engine and driveshaft components to selectively control torque and speed ratios between the crankshaft and driveshaft. In a manually operated transmission, a corresponding manually operated clutch may be interposed between the engine and transmission to selectively engage and disengage the crankshaft from the driveshaft to facilitate manual shifting among available transmission gear ratios.
On the other hand, if the transmission is automatic, the transmission will normally include an internal plurality of automatically actuate clutch units adapted to dynamically shift among variously available gear ratios without requiring driver intervention. Pluralities of such clutch units, also called clutch modules, are incorporated within such transmissions to facilitate the automatic gear ratio changes.
Moreover, the transmission may incorporate numerous sets of gears and the various gears may be structurally comprised of sun gears, intermediate gears such as planet or pinion gears supported by carriers, and outer ring gears. Specific transmission clutches may be associated with specific sets of the selectable gears within the transmission to facilitate the desired ratio changes.
For example, one of the clutch modules of an automatic transmission associated with first (low) and reverse gear ratios may be normally situated at the front of the transmission and closely adjacent the engine crankshaft. The clutch module may include a driving member and a driven member which may be disposed circumferentially about the driving member. The driving and driven members may be configured to operate in multiple modes and, in one non-limiting example, the driving member may be drivingly rotatable in only one direction, however, other modes may be possible. Alternatively or additionally, the driving member may be drivingly rotatable in a plurality of directions. Moreover, the driving member may be selectively locked to the driven member via an engagement mechanism such as a roller, a sprag, a pawl, or other known engagement mechanisms. Furthermore, the rotation of the driving member may be effective to directly transfer rotational motion from the engine to the driveline.
In some transmission systems, the driven member may be fixed to an internal case or housing of an associated planetary member of the automatic transmission. Under such circumstances, in a first configurational mode, the driving member may need to be adapted to drive in one rotational direction, but freewheel in the opposite direction, in a condition referred to as overrunning. Those skilled in the art will appreciate that overrunning may be particularly desirable under certain operating states, such as when a vehicle is traveling downhill or coasting. Under such circumstance, the driven member may occasionally have a tendency to rotate faster than the driving member. Allowing the driving member to overrun the driven member may provide protection against damage to the engine and/or transmission components.
In a second non-limiting mode, such as when a vehicle may be in reverse gear, the engagement mechanisms may be adapted for actively engaging in both rotational directions of the driving member, thus not allowing for an overrunning condition in either direction.